Physicians often recommend specific tests for pregnant women who are at risk of delivering a child with Down Syndrome. Unfortunately, the tests themselves can be risky, so researchers are developing more accurate ways to analyze blood. Their most recent efforts are very promising.
Down Syndrome, also called Trisomy 21, is caused by an extra 21st chromosome. Normally a fetus carries two of these chromosomes – one from the father and one from the mother. But in Down Syndrome, there is an extra chromosome. It’s a genetic birth defect that results in varying degrees of mental retardation.
There are ways that doctors can determine whether a pregnant woman is at risk for a Down Syndrome baby. These include the mother’s age (usually over 35) and a personal or family history of other children with a birth defect. Once that risk has been established, blood can be drawn to measure the levels of certain substances in the mother’s blood, including the following:
– human chorionic gonadotropin (hCG)
– maternal serum alpha fetoprotein (MSAFP)
The problem is, abnormal levels of these substances don’t actually identify Down Syndrome; they only point to an increased risk. The only way to really diagnose Down Syndrome is to examine the chromosomes, and that requires a sample of either amniotic fluid (obtained through amniocentesis) or a chorionic villus. Unfortunately, both amniocentesis and chorionic villus sampling are invasive procedures; they carry their own risk, however small, of miscarriage.
Physicians have long felt the need for a safer but also more accurate way of identifying Down Syndrome. A blood test would be ideal, and there has now been a method developed that can analyze the small amount of fetal DNA in the mother’s blood. The most recent research, with 60 pregnant women identified to be at risk for a fetus with Down Syndrome, showed that this new method has a 66% detection rate (confirmed with either an amniocentesis or physical exam after birth). There was only one false positive and one false negative.
The researchers are encouraged by these results. They’d like to refine the test to improve its accuracy even further. They would then do another study, with a larger group of women, before the test could be approved for everyday use.
Many women, even if they’re at risk for a child with Down Syndrome, don’t like the idea of amniocentesis because of its own risk. But it can be nerve-wracking, especially if you have other children with birth defects, to go through an entire pregnancy wondering if this child will share them. A blood test that could answer this question could be a source of comfort for both the physician and the parents.